Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Many existing braces, such as knee braces, are designed with rehabilitation in mind. Typically, natural knee joint motion is inhibited or constrained in some way. There is a different need, however, for new knee and other joint braces which can be used for other purposes. In one example, a person wearing a heavy backpack might benefit from a knee brace which not only provides stability but also reduces the load on the muscles of the knee, particularly the quadriceps. Indeed, when the knee bends, it would be beneficial to lower the load carried by the knee by applying an external extension torque. Energy stored during the bending action can be used to straighten the knee as well. When the leg swings forward for the next step, it would be advantageous if the knee brace applied appropriate flexion torque to help lift the foot, or that the brace operated freely, applying minimal torque to the leg.
Existing braces using one degree of freedom (DOF) hinges may be sensitive to alignment of the brace to the knee joint. This can be a problem for assistive (torque-producing) braces. Mismatch between the instantaneous center of rotation of the hinge and of the knee causes uncomfortable or dangerous loads on the knee as well as making the brace migrate down the leg. The mismatch may occur because the one DOF hinges are only an approximation of the motion of the knee and because of deflection of the flesh where the brace attaches to the leg.
Other existing braces may require rigid structure spanning between the medial and lateral hinges. This enforces a fixed width and makes the brace wider than might be necessary since it accommodates the width of the knee at the desired maximum flexion position. To avoid a sloppy fit and interference of the braces of the left and right legs, these braces typically require custom fitting to each user. Still other example braces may not allow twisting of the foreleg and can restrict a normal DOF of the leg. Such braces can be awkward to use and increase the likelihood of chafing and migration of the brace. Therefore, an improved brace system may be desirable.